I replaced by ECT sender on my 1995 LS400 preventatively (sensor sending coolant temp to cluster) with the exact OEM part from Lexus. No issues with prior sensor I believe it was the factory original. It now seems less “damped” as in temp needle rises faster, will be just a touch above “normal” resting position for initial driving, then once I get on highway and cruise it gently goes a touch down to rest at the mark where the prior sensor rested and just stay there with no fluctuation while on highway. We’re talking mm of fluctuation but enough that you see it. Anyone had that kind of experience?

 

The coolant needle should be a "dummy" needle, where it should register the same value across a pretty broad range of temperatures (like 160F to 220F or something absurd).

Hook up an OBD and get a direct reading - is the actual numerical value doing anything funky?



Can you explain more in detail? Pictured is the normal resting position for the needle

 

Thanks and I am going to get some live data per your recommendation. I replaced the sender without draining coolant (lost just a very small amount and topped it up) but maybe I should have done a proper bleed. Before, the needle would gradually rise and then be dead on the line mark just below where the needle is in your picture and never, ever move from there. Now it rises to where it is in your picture but on a long highway drive will then gently go down to that line where it rested before and stay dead on there. No other parts changed. Also I replaced all the capacitors in the cluster some months back and no weird behavior / no change in the temp needle after doing that so I’m 99 percent sure it’s something to do with the sender itself (new one is less damped?) or maybe I need to bleed the system.

 

I replaced mine years ago by the same method as well. How much coolant did you loose? I don't recall losing a substantial quantity at all, I don't think any even made it to the ground. I never bothered topping up.

I do find it quite peculiar though, the system should be designed to move the needle quite substantially once it exits the "range". I've never heard of such subtle movements before.